https://www.famousscientists.org/7-great-examples-of-scientific-discoveries-made-in-dreams/
Discovery of the Structure of Benzene and Aromatic Chemistry
August Kekulé had been worrying about how the atoms in benzene are arranged.
It was a tough problem, because the ratio of carbon and hydrogen atoms was unlike that seen in other hydrocarbon compounds.
On a cold night in 1865, he had been working on the problem in his room.
Unable to find a solution, he turned his chair to the fire and dozed.
He began dreaming of atoms dancing. Gradually the atoms arranged themselves into the shape of a snake. Then the snake turned around and bit its own tail.
The image of the snake, tail in its mouth, continued to dance before his eyes. When Kekulé awoke, he realized what the dream had been telling him:
Benzene molecules are made up of
rings of carbon atoms.
Understanding these aromatic rings opened up an extremely important, completely new field of chemistry – aromatic chemistry – and a new understanding of chemical bonding.